Si nanocrystals in silicon nitride: An ellipsometric study using parametric semiconductor models

Low-pressure chemical vapour deposited Si₃N₄/nc-Si/Si₃N₄ layers prepared on Si substrates were characterized by spectroscopic ellipsometry. Model Dielectric Function (MDF) was applied to obtain the thickness and the dielectric spectra of the middle nc-Si layer. Sensitive effect of the deposition time was obtained on the MDF parameters. A comparison is presented between the studied samples and reference materials.     

Labeling of a bifunctional monophosphinic acid DOTA analogue with <Superscript>111</Superscript>In: Radiochemical aspects and preclinical results

The complex formation of the bifunctional monophosphinic acid DOTA analogue DO3AP^ABn (1,4,7,10-tetraazacyclododecane-4,7,10-triacetic-1-{methyl[(4-aminophenyl)methyl] phosphinic acid}) with ¹¹¹In at a tracer level was analyzed. Formation of a complex between ¹¹¹In and DO3AP^ABn was very rapid even at room temperature and high radiolabeling yields were achieved. As introducing the methylphosphinic acid arm to the DOTA structure generated a chiral centre, more than one peak (probably corresponding to various diastereoisomers) of ¹¹¹In-DO3AP^ABn were separated on HPLC. Four peaks were separated by HPLC, they probably correspond to four diastereoisomers of ¹¹¹In-DO3AP^ABn originating from combination of chirality of complexes of DOTA-like ligands with chirality of coordinated phosphorus atom. Studies in rats showed rapid elimination of radioactivity from the blood and other organs and tissues. The results indicate that DO3AP^ABn represents a promising ligand for radiolabeling of target-specific biomolecules with radiometals.     

Optical and X-ray characterization of ferroelectric strontium-bismuth-tantalate (SBT) thin films

Metal-organic chemical vapor deposition (MOCVD) made layers of strontium-bismuth-tantalate (SBT) were characterized by spectroscopic ellipsometry (SE) using the Adachi model [S. Adachi, Phys. Rev. B 35 (1987) 7454-7463]. The evaluated optical parameters were correlated with the physical and chemical behavior examined by X-ray diffraction (XRD).As a result, it was possible to fit the measured spectra with the Adachi model in a wide range covering the region of the band gap. The Adachi model provides electronic layer parameters like the transition energy E₀ and broadening Γ. Our investigations established a correlation between XRD-determined average grain size and the electronic layer parameters.     

Guest diffusion in interpenetrating networks of micro- and mesopores

Pulsed field gradient NMR is applied for monitoring the diffusion properties of guest molecules in hierarchical pore systems after pressure variation in the external atmosphere. Following previous studies with purely mesoporous solids, also in the material containing both micro- and mesopores (activated carbon MA2), the diffusivity of the guest molecules (cyclohexane) is found to be most decisively determined by the sample "history": at a given external pressure, diffusivities are always found to be larger if they are measured after pressure decrease (i.e., on the "desorption" branch) rather than after pressure increase (adsorption branch). Simple model consideration reproduces the order of magnitude of the measured diffusivities as well as the tendencies in their relation to each other and their concentration dependence.     

Solving sparse non-negative tensor equations: algorithms and applications

We study iterative methods for solving a set of sparse non-negative tensor equations (multivariate polynomial systems) arising from data mining applications such as information retrieval by query search and community discovery in multi-dimensional networks. By making use of sparse and non-negative tensor structure, we develop Jacobi and Gauss-Seidel methods for solving tensor equations. The multiplication of tensors with vectors are required at each iteration of these iterative methods, the cost per iteration depends on the number of non-zeros in the sparse tensors. We show linear convergence of the Jacobi and Gauss-Seidel methods under suitable conditions, and therefore, the set of sparse non-negative tensor equations can be solved very efficiently. Experimental results on information retrieval by query search and community discovery in multi-dimensional networks are presented to illustrate the application of tensor equations and the effectiveness of the proposed methods.     

Zur Methodik der Konzentrationsmessungen an Polymerl?sungen bei den Adsorptionsuntersuchungen

Ohne Zusammenfassung     

Background gradient suppression in stimulated echo NMR diffusion studies using magic pulsed field gradient ratios

By evaluating the spin echo attenuation for a generalized 13-interval PFG NMR sequence consisting of pulsed field gradients with four different effective intensities (F(p/r) and G(p/r)), magic pulsed field gradient (MPFG) ratios for the prepare (G(p)/F(p)) and the read (G(r)/F(r)) interval are derived, which suppress the cross term between background field gradients and the pulsed field gradients even in the cases where the background field gradients may change during the z-store interval of the pulse sequence. These MPFG ratios depend only on the timing of the pulsed gradients in the pulse sequence and allow a convenient experimental approach to background gradient suppression in NMR diffusion studies with heterogeneous systems, where the local properties of the (internal) background gradients are often unknown. If the pulsed field gradients are centered in the tau-intervals between the pi and pi/2 rf pulses, these two MPFG ratios coincide to eta=G(p/r)/F(p/r)=1-8/[1+(1/3)(delta/tau)(2)]. Since the width of the pulsed field gradients (delta) is bounded by 0< or =delta< or =tau, eta can only be in the range of 5< or =-eta< or =7. The predicted suppression of the unwanted cross terms is demonstrated experimentally using time-dependent external gradients which are controlled in the NMR experiment as well as spatially dependent internal background gradients generated by the magnetic properties of the sample itself. The theoretical and experimental results confirm and extend the approach of Sun et al. (J. Magn. Reson. 161 (2003) 168), who recently introduced a 13-interval type PFG NMR sequence with two asymmetric pulsed magnetic field gradients suitable to suppress unwanted cross terms with spatially dependent background field gradients.     

C~*-代数的Murray-von Neumann分类理论的抽象架构

Murray和von Neumann在对W~*-代数进行分类工作时,主要的工具是刻画W~*-代数中的投影的性质(事实上,W~*-代数是由投影所生成的).因为一般的C~*-代数可能不包含任何非零的投影,所以不能将Murray和von Neumann的方法,直接地应用到C~*-代数上来得出分类理论.本文作者在最近的两项工作中,分别使用C~*-代数的开投影和正元来代替投影,得到两套平行的Murray-von Neumann式的分类理论.本文在简单描述了这两套分类理论之后,将会给出一个一般的分类架构,它可以用来得出好些C~*-代数的分类理论(包括我们之前的两套理论),我们也会通过它来讨论各种分类理论之间的等价性,并给出之前两套理论的细化.     

Anticorrelation between Surface and Subsurface Point Defects and the Impact on the Redox Chemistry of TiO2(110)

By using a combination of scanning tunneling microscopy (STM), density functional theory (DFT), and secondary‐ion mass spectroscopy (SIMS), we explored the interplay and relative impact of surface versus subsurface defects on the surface chemistry of rutile TiO₂. STM results show that surface O vacancies (V_O) are virtually absent in the vicinity of positively charged subsurface point defects. This observation is consistent with DFT calculations of the impact of subsurface defect proximity on V_O formation energy. To monitor the influence of such lateral anticorrelation on surface redox chemistry, a test reaction of the dissociative adsorption of O₂ was employed and was observed to be suppressed around them. DFT results attribute this to a perceived absence of intrinsic (Ti), and likely extrinsic interstitials in the nearest subsurface layer beneath inhibited areas. We also postulate that the entire nearest subsurface region could be devoid of any charged point defects, whereas prevalent surface defects (V_O) are largely responsible for mediation of the redox chemistry at the reduced TiO₂(110).